Apparatus for thermal treatment of minerals



Dec. 17, 1968 CHABAGLIYAN 3,416,778

APPARATUS FOR THERMAL TREATMENT OF MINERALS- Filed March 29, 1967 to 2Sheets-Sheet 1 INVENTOR. HENRI FERNAND CHABAGLIAN Dec. 17, 1968 H. F.CHABAGLIAN 3,416,778

APPARATUS FOR THERMAL TREATMENT OF MINERALS Filed March 29, 1967 2Sheets-Sheet 2 INVENTOR.

HENRI FERNAND GHABAGLIAN United States Patent 3,416,778 APPARATUS FURTHERMAL TREATMENT OF MINERALS Henri Fernand Chabaglian,Maisons-Laflitte, France, as-

signor to Poiysius G.m.b.H., Neubeckum, Westphalia, Germany Filed Mar.29, 1967, Ser. No. 626,736 Claims priority, application France, May 6,1966,

4 Claims. Cl. 26332) ABSTRACT OF THE DISCLOSURE Background of theinvention The invention relates to apparatus for thermal treatment ofminerals which have been sized or shaped by tumbling, pelleting,briqueting or any other process.

The known apparatus utilizes one or more traveling grills whichtransport the material toward a rotary kiln where the roasting itself isconducted, while on the grill, preceding the kiln, the material isheated by hot gases discharged from the kiln.

In certain apparatus the kiln is preceded with a traveling grill throughwhich the gas makes two passes, i.e., the \grill is separated into twoparts, the hot gases recuperated from the downstream part being suppliedto the upstream part of the grill.

In other apparatus, the kiln is preceded by two grills in cascade, thefirst serving as a recuperator for the heat radiated from the kiln andfrom the cooler, and the second serving as recuperator for the heat ofthe gases discharged from the kiln. In this apparatus the circuit of thegas is independent and forms a simple gas passage.

These devices for thermal treatment have given good results in manycases, but they are nevertheless limited by the maximum dimensions whichit is technically feasible to give to the traveling grill.

Moreover, when the hot gases are derived principally from the kiln, itis necessary to have a large volume of gas flowing through the kiln, sothat because of the dimensions of the kiln and the intensity of thecurrent of gas, clouds of dust are created with resultant danger ofincrustation of the apparatus.

Summary of the invention The object of the invention is to provide aheat treatment apparatus of the type hereinbefore described in 'whichthe circulation and the recuperation of the hot gases permits greaterflexibility of treatment by separating the functions of drying andpreheating and assuring an improvement in the efficiency of heating onthe grills, as well as an increase in capacity which is difiicult toobtain by merely increasing the dimensions of the grills.

The invention then comprises apparatus for thermal treatment of mineralscharacterized in that it comprises a first traveling grill for drying onwhich the material is heated by gases which have passed through a secondpreheating grill on which the material is heated partly by gasesdischarged from the kiln and partly by burners which are supplied withsecondary air of combustion consisting of hot air discharged from acooler which follows the kiln, a burner in the kiln being also suppliedwith secondary air consisting of part of the hot air discharged from thecooler.

Other auxiliary features of the invention will appear from the followingdetailed description, in which reference is had to the annexed drawings.It will be understood that the description and the drawings are givenonly by way of example and are not intended to limit the scope of theinvention.

Brief description of the drawings FIGURE 1 is a schematic view of anapparatus according to the invention.

FIGURE 2 is a schematic view of a modification of the apparatusaccording to the invention which is shown in FIGURE 1.

Description of the preferred embodiments According to the invention, theapparatus for thermal treatment shown in FIGURE 1 comprises a conveyor 1which conducts the material to be treated into a hopper 2 whichdistributes it upon a first traveling grill 3, which transports thematerial across a drying chamber 4 and discharges it into a hopper 5which distributes the dry material upon a second traveling grill 6.

The role of this intermediate hopper 5 is to form a reservoir ofmaterial between the two grills 3 and 6 in order that the grill 6 may besuitably covered with the material.

Furthermore, this hopper 5 on the one hand tends to cause the materialto be turned over in the course of its transfer, thus permitting betterequalization of the temperatures in the mass of the material, and on theother hand tends to stir the material so as to cause segregation of thefine particles or small fragments of material, the elimination of which,When necessary, can be obtained by using a hopper wall 7 consisting of ascreen.

This hopper 5 thus makes possible a speed of travel of the materialwhich is different on the two grills, so that the thickness of the layerof the material may be different on each grill, the height of the layerupon the grill 6 being determined by an adjustable regulator 8, while alevel detector 9, which may consist of a sound transmitter and a soundreceiver, for example, permits the determination of the quantity ofmaterial in the hopper 5.

The difference in the speed of travel of the material on the two grillswhich is made possible by the hopper thus permits adjustment of theduration of treatment in accordance with the requirements of thematerial being treated.

Material on the grill 6 then passes through the precalcination chamber10 and is transferred into a rotating kiln 11, where the actual roastingtakes place, after which the material is discharged upon a grill 12where it is cooled while passing through three successive chambers, 13,14 and 15.

The air which is used for final cooling in the exit chamber '15 isdischarged to the exterior at a temperature of about to 200 C.

The air which is used for intermediate cooling in the intermediatechamber 14 at about 200400 C. is withdrawn by a fan 16 and conducted tothe chamber 10, where it is used as air of combustion for the burners17.

Air which is used for the initial cooling of the material in the inletchamber 13, at about 800-1 100 C., is discharged into the kiln 11adjacent a burner 18, to serve as secondary air of combustion for theburner 18, which is also supplied with primary air, at the head of thekiln 11.

Gases at about 1000-1200 C. from the kiln 11 pass into the chamber 10,where they are mixed with the gases flowing from the burners 17, andpass through the bed of material to bring the material to an averagetemperature of 700 C. at which the principal reactions for changing thestate of the material commence (between 500 and 900 0., according to thematerial) such as decarbonation, dehydration, oxidation or others.

In a chamber 19 under the grill 6, the gases at 200- 400 C., which havepassed through the bed of material, are withdrawn through a dustcollector 20 by a fan 21 which discharges them into the chamber 4.

The gases discharged by the fan 21 then pass through the bed of materialdisposed upon the grill 3, to penetrate into a chamber 22 at atemperature of 80120 C., from which they are withdrawn by a fan 23 whichdischarges them to the exterior by a stack 24.

It will be noted that upon the drawing the flow of the material isindicated by solid arrows, while the flow of the gases is indicated bydashed arrows.

The apparatus according to the invention permits great flexibility ofthe thermal treatment.

Because of the fact that the sensible heat which can be recovered in thecooler is extracted, it becomes useful to furnish the necessarycombustibles for the entire process partly at the head of the rotarykiln 11, by means of the burner 18, and partly upon the precalcinationgrill 6 by means of the burners 17 when the thermal requirements in thekiln 11 are substantially less than those necessary in the chambers 10and 14, for example:

For pelleting of a rich hematite, the requirements in the kiln 11 are ofthe order of 140 Th., and the thermal requirements in the chambers 4 and10 are of the order of 310 Th.

For the pellting of a magnetite concentrate, the requirements in thekiln 11 are of the order of 128 Th. The thermal requirements in thechambers 4 and 10 are of the order of 200 Th.

For the pelleting of a calcareous minette of Lorain, the requirements inthe kiln 11 are of the order of 190 Th., and the requirements in thechambers 4 and 10 are of the order of 540 Th.

Forthe roasting of an artifical cement, the requirements in the kiln 11are of the order of 520 Th., and the requirements in the chambers 4 and10 are of the order of 550 Th.

In the first three cases cited, the thermal requirements in the kiln aresubstantially less than those necessary in the chambers 4 and 10.

In accordance with the invention, it is desirable to furnish thecombustibles partly at the head of the kiln by means of the burner 18,and partly at the chamber 10 by means of the burners 17. Thisdistribution may vary between one-third and two-thirds of the total ateach of the points 18 and 17, depending upon the material treated.

For the fourth case cited, the thermal requirements are substantiallythe same in the kiln 11 and in the chambers 4 and 10. The distributionmakes it possible to limit the gas flow between the kiln 11 and thechamber 10, to prevent raising dust. When the treatment of the materialrequires high temperatures, and in order not to treat the material toolong in the rotary kiln where the material is subjected to agitationwhich impairs the cohesion, one may carry the material on the secondgrill to an elevated temperature of about 1200" C., in which case it isdesirable, for mechanical and economical reasons, to employ a secondgrill which is short. Also, the material arriving upon this second grillshould already be at a temperature which is relatively high, about 600to 900 C., so that it is desirable to employ a modification of theabovedescribed apparatus, which modification is represented by the formof the apparatus illustrated in FIGURE 2.

According to this form of the apparatus embodying the invention, shownin FIGURE 2, the first grill 3 is a grill which is subjected to twopasses of the gas, and

which travels through two chambers, the drying chamber 4 followed by apreheating chamber 25 which receives the gases discharged from thechamber 19 under the second grill 6.

These gases, after having passed through the bed of material, pass intoa chamber 26 under the grill 3, from which they are withdrawn through adust collector 27 by a fan 28 which discharges them into the chamber 4.

Thus all of the relative advantages of FIGURE 2 are retained, while thecost of the installation is reduced substantially by comparison withcontinuous installations which employ only one grill.

The invention is not limited only to the modes of realization which havebeen described and shown, but covers all other variations thereof.

I claim:

1. Apparatus for thermal treatment of minerals comprising a rotary kilnpreceded by traveling grills for drying and preheating, wherein theimprovement comprises a first traveling grill for drying; a secondtraveling grill for preheating, the inlet end of which is arranged toreceive material discharged from the exit end of the first grill, andthe exit end of which is arranged to discharge material into the inletof the kiln; an enclosed cooler arranged to receive material dischargedfrom the exit of the kiln; two separate chambers adjacent to the twoends of the first grill, which are bounded by the upper surface of thegrill; two separate chambers adjacent to the two ends of the first grillwhich are bounded by the lower surface of the grill; a separate chamberbounded by the upper surface of the second grill; a separate chamberbounded by the lower surface of the second grill; a burner in the kiln;an inlet for supplying air to the cooler; a recuperating system forwithdrawing the air which has been heated in the cooler and supplying aportion thereof as secondary combustion air to the kiln and anotherportion thereof to one of the chambers associated with the second grill;said chamber containing a burner and having a connection through whichit receives hot gases discharged from the kiln; and another recuperatingsystem for withdrawing, from the other chamber associated with thesecond grill, gases which have passed through the grill, and forsupplying such gases to one of the chambers adjacent to the exit end ofthe first grill; the other chamber adjacent to the exit end of the firstgrill being provided with a recuperating system for withdrawing fromsuch chamber gases which have passed through the adjoining portion ofthe first grill and for supplying such gases to one of the chambersadjacent to the inlet end of the first grill to cause such gases to passthrough the other portion of the first grill.

2. Apparatus :for thermal treatment of minerals comprising a rotary kilnpreceded by traveling grills for drying and preheating, wherein theimprovement comprises a first traveling grill for driving; a secondtraveling grill for preheating, the inlet end of which is arranged toreceive material discharged from the exit end of the first grill, andthe exit end of which is arranged to discharge material into the inletof the kiln; an enclosed cooler which is divided into an inlet chamberarranged to receive material discharged from the exit of the kiln, anintermediate chamber which receives material from the inlet chamber, andan exit chamber which receives material from the intermediate chamber; aseparate chamber bounded by the upper surface of each of the grills; aseparate chamber bounded by the lower surface of each of the grills; aburner in the kiln; inlets for supplying cooling air to all threechambers of the cooler; a recuperating system for withdrawing, from theintermediate chamber of the cooler, air which has been heated to anintermediate temperature, and for supplying such air to one of thechambers associated with the second grill; such associated chambercontaining a burner and having a connection through which it receiveshot gases discharged from the kiln; and another recuperating system forwithdrawing, from the other chamber associated with the second grill,gases which have passed through the grill, and for supplying such gasesto one of the chambers associated with the first grill to cause suchgases to pass through the first grill; the inlet chamber of the coolerhaving a connection through which air which has been heated in suchinlet chamber to a temperature higher than such intermediate temperatureis supplied as secondary combustion air to the kiln; and the exitchamber of the cooler having an outlet for exhausting air Which has beenheated in such exit chamber.

3. Apparatus according to claim 2 wherein a hopper is arranged toreceive the material passing from the first grill to the second grill,for controlling the thickness of References Cited UNITED STATES PATENTS1,468,168 9/1923 Pike 26332 3,254,882 6/1966 Helming 26332 3,313,5344/1967 Frans 26332 FREDERICK L. MATTESON, JR., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

